Alternating current switch



May 27, 1969 E. K. HOWELL ALTERNA'IING CURRENT SWITCH Sheet Filed March23. 1966 FIG. 1

FIG. 2

)X/QZIw/e. A/E/TI-I HOWELL av 20M A 7' TORA/EV E. K. HOWELL ALTERNAIINGCURRENT SWITCH May 27, 1969 Filed um 23. 1966 Sheet United States PatentUS. Cl. 307-252 28 Claims This invention relates to an alternatingcurrent switch which includes a semiconductive bidirectional devicehaving at least one gate terminal, as the current interrupting element.More specifically it relates to an alternating current switch includinga semiconductive bidirectional device as the current interruptingelement, and a circuit associated with the gate terminal for causing thedevice to assume its low impedance characteristic, and to indefinitelyretain this characteristic, until it is again desirable for the devicetoassume its normal or high impedance characteristic.

A relatively recent addition to the growing family of semiconductivedevices broadly referred to as semiconductors, are the bidirectionaltriode P-N-P-N switches. These bidirectional triode switches areprovided with two main current carrying terminals and at least one gateor trigger terminal. Current flow from the two main current carryingterminals through the bidirectioanl triode switch in either directioncan be controlled by the application of a low voltage, low current pulsebetween a gate terminal and one of the load current terminals. Thesedevices have some similarity to the earlier developed silicon-controlledrectifiers. They are similar in their blocking current and voltagecharacteristics. But, unlike silicon-controlled rectifiers, they canswitch load current of either polarity. For a more complete discussionof the bidirectional triode P-N-P-N switches reference may be made to anarticle entitled: Bi-Directional Triode P-N-P-N Switches, Gentry, F. E.,et al., in the Proceeding of the IEEE, volume 53, No. 4, April 1965, pp.355-369. Bidirectional triode P-N-P-N switches are also discussed in abook entitled: Semiconductor Controlled Rectifiers Principles andApplications of P-N-P-N Devices by Gentry, F. E., et al., published byPrentice-Hall, Inc., Englewood Cliffs, N.J., 1964.

This invention is particularly directed toward utilizing asemiconductive bidirectional device such as a bidirectional triodeP-N-P-N switch as an A.C. switch. An A.C. switch which would eliminatethe need for mechanically movable contacts to interrupt a load currentwould be highly desirable in some applications. The combination of asemiconductive bidirectional device having two main current carryingterminals and at least one additional gate terminal and a circuitarrangement which provides at the desired time a low voltage, lowcurrent signal to the gate terminal, would provide such an A.C. switch.That is, an arrangement whereby an initiating signal is applied to thegate of a bidirectional triode, to cause the triode to conduct, a signalis maintained on the gate, such that the bidirectional triode willcontinue to conduct through an indefinite number of full cycles ofalternating current even though the initiating signal which initiallyturned on the triode is removed, and the signal maintained on the gateis removed to cause the triode to stop conducting.

It is therefore an object of this invention to provide a novel andimproved A.C. switch utilizing a semiconductive bidirectional devicehaving two main current carrying terminals and at least one additionalgate terminal, in a circuit arrangement whereby a momentary signal maybe provided to cause the bidirectional device to assume its lowimpedance characteristic and to retain this low impedance characteristicafter the removal of the momentary signal.

It is another object of this invention to provide an alternating currentswitch having two main current carrying terminals and at least oneadditional gate terminal, including a semiconductive bidirectionaldevice in a circuit arrangement whereby a first momentary signal willcause the bidirectional conducting device to assume its low impedancecharacteristic, thereby conducting current, and whereby thebidirectional device may be returned to its high impedance state by asecond momentary signal.

It is a further object of this invention to provide a control 'means forenergizing a load from an A.C. supply including in a circuit arrangementa semiconductive bidirectional conducting device having two main currentcarrying terminals and at least one additional agate terminal, and theload, such that the variation of a first variable impedance will causethe semiconductive device to assume its low impedance characteristic andsuch that the device will continue to exhibit its low impedancecharacteristic until the impedance of a second variable impedance deviceis varied, at which time the device will again assume its high impedancecharacteristic.

These objects are accomplished in accordance with this invention, in oneform thereof, by providing a circuit arrangement including therein asemiconductive bidirectional device having two main current carryingterminals and at least one additional gate terminal. The main currentcarrying terminals are connected in series with a circuit energized byan A.C. source. Typically the device will be connected in series with aload, the energization of which is to be controlled by the conductivestate of the device. The circuit arrangement further includes a controlcircuit including a variable impedance device and energy storage meansconnected in series. This control circuit is connected in parallel withthe device such that the A.C. source simultaneously energizes both thedevice and the control circuit. The junction of the variable impedanceand the energy storage means is connected by :a gate circuit to the gateterminal of the device.

With the variable impedance in a high impedance state, insufiicientcurrent is conducted through the variable impedance and the gate circuitto apply a signal of greater than a predetermined level which isnecessary to cause the device to assume its low impedancecharacteristic. A decrease in the impedance of the variable impedancebelow a predetermined level, will permit a signal greater than thepredetermined level to be applied to the gate of the device, therebycausing the device to assume its low impedance characteristic. While thedevice is in its low impedance state, the energy storage means willreceive energy through the gate terminal and the gate circuit from theA.C. source. As the A.C. source passes through a voltage zero, whichwould also be a current zero in the case of a resistive load, thecurrent flowing through the energy storage means, the gate circuit, andthe gate terminal, will be of a magnitude sutficient to provide a signalof greater than the predetermined magnitude to the gate of the devicesuch that the device will retain its low impedance characteristic duringthe following half cycle. This current flow in the gate circuit duringsupply voltage zeros is due to the fact that the energy storage meanscauses the current flow in the gate circuit to be out of phase with theA.C. source voltage. Due to this out of phase current flow, the devicemaintains its low impedance characteristic as long as the circuitconnections to the A.C. source are uninterrupted. Thus, a momentarydecrease below a predetermined level of the impedance of the variableimpedance will cause the device to be latched in its low impedancecharacteristic.

A second variable impedance is provided to dissipate the energy in theenergy storage means when it is desirable for the device to again assumeits high impedance characteristic. Reducing this second variableimpedance below a predetermined level will cause the energy in theenergy storage means to be dissipated below the level which provides agate signal of greater magnitude than the predetermined magnitudenecessary for the device to maintain its low impedance state.

Other objects and further details of that which is believed to be noveland the invention will be clear from the following description andclaims taken with the accompanying drawings wherein:

FIGURE 1 is a circuit diagram of a first embodiment of this inventionemploying a capacitor as the energy storage means.

FIGURE 2 is a circuit diagram of a second embodiment of this inventionemploying an inductor as the energy storage means.

FIGURE 3 is a circuit diagram of the first embodiment of this inventionmodified to employ a different arrangement of the variable impedancemeans.

FIGURE 4 is a circuit diagram of the first embodiment of this inventionmodified to employ an arrangement of the variable impedance meansdiffering from those shown in FIGURES l and 2.

FIGURE 5 is a circuit diagram of the first embodiment of this inventionmodified to employ an arrangement of the variable impedance meansdiffering from those shown in FIGURES l, 3, and 4.

Referring to the circuit diagram of FIGURE 1 the operation of an A.C.switch or as it may be referred to, a control circuit for energizing aload from an A.C. supply will be described. The control circuit shownenclosed within the dotted lines 2 is energized by connecting its twoexternal terminals 4 and 6 to an A.C. supply. Terminals 8 and 10representing an A.C. supply (not shown) are connected to terminals 4 and6 with a control switch 12 interposed between terminals 4 and 8. Thecontrol circuit includes a semiconductive bidirectional device 14connected in series with an impedance 16 between terminals 4 and 6. Thesemiconductive bidirectional device is shown as having main currentcarrying terminals 18 and 20, and a gate or trigger terminal 22. Thedevice shown is commonly called a triac and by InternationalElectrotechnical Commission standards named a bidirectional triodethyristor. While this particular device is shown, which will hereinafterbe referred to as a triac, any other semiconductive bidirectional devicewhich has at least one gate terminal, may be employed. It is onlynecessary that the semiconductive bidirectional device which is employedexhibit a high impedance characteristic in the absence of a signal of apredetermined amplitude at its gate, and that it exhibit a low impedancecharacteristic in the presence of a signal of a magnitude greater thanthe predetermined amplitude at its gate.

The gate terminal 22 of the triac 14 is energized by a gate circuitwhich is in turn energized by a control circuit. The control circuit isshown as including a resistor 24, a switch 26, and a capacitor 28connected in series between the terminals 4 and 6. The series circuitcomprising resistor 24 and switch 26 may be replaced by any variableimpedance means. Such a variable impedance might be a semiconductivedevice such as a transistor or a semiconductor controlled rectifier. Anembodiment of this invention utilizing a semiconductor controlledrectifier will be discussed later. The capacitor 28 may be replaced byany other energy storage means which it might be desirable to utilize,such as an inductor. As shown in FIGURE 1, the gate circuit comprises aresistor 30 connected between the control terminal 22 and a junction 32between the switch 26 and the capacitor 28. The gate circuit may be adirect connection as will be discussed in another embodiment of thisinvention.

Before setting forth the operation of the circuit just described, atypical use of the circuit as a control circuit will be set forth. In atypical application, the impedance 16 may be a resistive load such as alamp in a single luminaire, or it may be representative of all the lampsin all the luminaires and a room or hall. The control circuit and load16 shown enclosed within the dotted lines 2 would in the case of asingle lamp be contained within the outlet box on which is mounted thesocket for the lamp. Terminals '4 and 6 would be connected to the A.C.supply system represented by terminals 8 and 10. Terminal 4 beingconnected to terminal 8- through a wall switch 12 and terminal 6 beingdirectly connected to terminal 10.

Assuming that the wall switch 12 has been open, the triac 14 will remainin its high impedance state uponthe closing of wall switch 12 if switch26 remains in its normally opened position. Switch 26, the contacts ofwhich wouldbe in the outlet box, would in the usual case be remotelyactuated. Examples of such remote means for closing the switch 26 willbe further discussed in the following embodiments. Closing the switch 26will cause a signal of greater than the predetermined amplitude to beapplied to gate 22 through resistor 30. With the application of thiscontrol signal, the triac 14 assumes its low impedance characteristic,i.e., is turned on so as to conduct. With the triac 14 turned on, theload 16 is energized from the A.C. supply.

The triac 14 would normally revert to its high impedance characteristic,i.e., turn off, during the next succeeding current zero of the supply ifthe switch 26 were only closed momentarily. But, the arrangement of thecontrol circuit and gate circuit as shown in FIGURE 1 insures that thetriac will continue to conduct until the switch 12 is open. This is dueto the fact that a signal of greater than the predetermined amplitude ismaintained on'the gate 22 by the control and gate circuits. Currentlimiting 24 protects the capacitor 28 from the damaging effects of anexcessive charging current which it would draw from the AC. supply onthe closing of switch 26. After the triac begins conducting load currentbetween its main current carrying terminals 18 and 20, the gate currentwill also flow between main terminal 18 and gate terminal 22. This gatecurrent which flows through resistor 30 to charge capacitor 28, resultsfrom the voltage appearing across the triac 14 and the load 16. Thisvoltage is essentially the A.C. supply voltage, most of which appearsacross the load 16. This gate current is limited by resistor 30 in thegate circuit. With a highly resistive load 16, the gate current, due tothe capacitor 28, will be out of phase with the load current.

Sufficient energy in the form of a charge on capacitor 28 is storedduring the period load current is flowing, to assure a gate signal ofgreater than the predetermined magnitude after the supply passed througha zero, so as to cause the triac to conduct during the succeeding halfcycle. Due to the bidirectional nature of the device, the capacitor 28will continue to supply gate signals greater than the predeterminedamplitude to the gate 22 through resistor 30 during succeeding loadcurrent zeros, such that the triac 14 will be latched on to continuouslyconduct between its main current carrying terminals without need foradditional closures .of switch 26. Thus, it is only necessary thatswitch 26 be closed momentarily to latch the triac in its low impedancecharacteristic.

The load 16 may be deenergized by opening switch 12 or, if it isdesirable to be able to remotely deenergize the load 16, an additionalvariable impedance turn-off circuit may be provided. This circuit, whichis shown as comprising a switch 34, is connected between the junctionpoint 32 and a second junction point 36 between one terminal of the load16 and main terminal 20 of the triac. Switch 34 is normally open, wouldbe remotely actuated in the same manner as switch 26. Closing thecontacts of switch 34 causes capacitor 28 to be discharged through theload 16, such that an insufficient charge is retained thereon to supplya gate signal of greater than the predetermined value after the nextsucceeding current zero. Thus, the triac will return to its rightimpedance characteristic at the next succeeding current zero, therebydeenergizing the load 16.

Considering now the circuit diagram of FIGURE 1 as representing an A.C.switch, the impedance 16 will no longer represent the load. Rather, aload (not shown) and an A.C. supply (not shown) are connected in seriesbetween the terminals 8 and 10. The impedance 16 rather than being aload, is a very small impedance. With impedance 16 very small, as is theimpedance of triac 14 when conducting, the current fiow betweenterminals 4 and 6 is determined by the TC. supply voltage and the loadimpedance. For a predetermined load and a predetermined A.C. supplyvoltage, a predetermined current will flow through the triac 14 and thevery small impedance 16. The impedance 16 is chosen such that thevoltage developed across it due to the current flowing therethroughwill, along with the voltage developed across the triac 14 between thegate terminal 22 and main current carrying terminal 20, produce asuflicient voltage across the series circuit comprising the triac gate14, resistor 30, and capacitor 28, to charge capacitor 28 to asufiicient level to provide a gate signal greater than the predeterminedamplitude to maintain the triac 14 in its low impedance state afterswitch 26 has been closed momentarily. In this arrangement, it isnecessary to determine the impedance value of impedance 16 for a givenload current, so as to insure sufficient energy storage in the capacitor28 to provide a gate signal of greater than the predetermined amplitude.Since the voltage appearing across the series circuit comprising theresistor 30 and the capacitor 28 is greatly reduced in this arrangement,the resistor 30 may be of a very small value or replaced by a conductor.

In still aonther embodiment of the A.C. switch, the impedance 16 may bemade negligible, that is replaced by a conductor. In this arrangementthe resistor 30 is also replaced by a very small impedance or aconductor. The charging current for the capacitor 28 through the gateterminal is derived from the voltage drop appearing across the triacbetween the terminals 18 and 20. The gate terminal 22 assumes thevoltage of main current carrying terminal 18 while the triac is in itslow impedance state, such that the voltage drop between main currentcarrying terminals 18 and 20 due to load current appears between gateterminal 22 and main current carrying terminal 20. Due to the smallvoltage available for charging capacitor 28, the triac 14 must beresponsive to a very low voltage, low current gate signal.

Referring now to FIGURE 2, an alternate embodiment of the invention isshown in which the energy storage means shown as capacitor 28 in FIGURE1 is replaced by an inductor 28. Also, the gate circiut is shown ascomprising a direct connection between the control terminal 22 of thetriac 14 and junction 32. The operation of this alternate embodiment ofthe invention is quite similar to that shown in FIGURE 1.

Assuming that the switch 12 has been open, the triac 14 will remain inits high impedance state upon the closing of switch 12 if switch 26remains in its normally open position. Closing the contacts of switch 26will apply a control signal having a greater amplitude than thepredetermined amplitude to gate terminal 22. This control signal willturn triac 14 on, thereby energizing the load 16 from the A.C. supply.

As did the capacitor 28 in FIGURE 1, inductor 28' will store suflicientenergy due to gate current flow to provide a gate signal of greater thanthe predetermined magnitude immediately after a supply voltage zero soas to cause the triac to coninue to conduct after the supply voltagepasses through a voltage zero. A resistor 30 is not needed in the gatecircuit, since the inductor 28' will itself limit the gate current.

As was discussed with respect to FIGURE 1, the portion of the circuitincluded within dotted line 2 may be considered an A.C. switch when theload (not shown) and an A.C. supply (not shown) are connected in seriesbetween terminals 8 and 10. Again, the impedance 16 may be very small orreplaced by a negligible impedance that is, a conductor.

Referring now to FIGURE 3, an embodiment of the invention in which theswitch 26 in the control circuit and the switch 34' in the turn-offcircuit are remotely controlled will be described. In this embodiment,the switches 26' and 34 are made responsive to a carrier frequencyimposed on the A.C. supply (not shown) represented by the terminals 8and 10. More particularly, the switch 26 is a pair of normally opencontacts of a relay 38 which also includes an actuating coil 40.Similarly, switch 34' is a pair of normally open contacts of a relay 42which also includes an actuating coil 44. The actuating coil 40 of relay38 is connected in series with a capacitor 46 between terminals 4 and 6.The capacitance of the capacitor 46 is chosen such that the seriescircuit including actuating coil 40 and capacitor 46 is resonant at afirst predetermined frequency. Similarly, the actuating coil 44 of relay42 is connected in series with a capacitor 48 between terminals 4 and 6.The capacitance of capacitor 48 is chosen such that the series circuitincluding actuating coil 44 and capacitor 48 is resonant at a secondpredetermined frequency.

While relays 38 and 42 may be of many varied types, resonant reedrelays, and relays formed of reed switches and actuating coils would beparticularly suitable. The resonant reed relays would be chosen to haveresonant frequencies corresponding to the first and second predeterminedfrequencies. Relays formed of reed switches and actuating coils would bedesigned such that the read switches would only be actuated in responseto the increased resonant current flows at the first and secondpredetermined frequencies.

The first and second predetermined frequencies are chosen to besubstantially higher than the supply frequency, such as are commonlyreferred to as a carrier frequencies. The switch 12 is not necessary foroperation of the control circuit shown in FIGURE 2 but, may be providedfor manual deenerigaztion of the load 16. With the switch 12 closed,imposing a carrier frequency signal corresponding to the firstpredetermined frequency on the A.C. supply represented by terminals 8and 10 will energize the actuating coil 40 to a sufficient level toclose contacts 26', thereby causing triac 14 to turn on as previouslydiscussed with respect to FIGURE 1. To close contacts 34', therebyturning off triac 14, a carrier frequency signal corresponding to thesecond predetermined frequency is imposed on the A.C. supply representedby the terminals 8 and 10. The carrier frequency signals correspondingto the first and second predetermined frequencies need be maintainedonly momentarily to turn the triac 14 on or off respectively. If it isdesirable to provide for only remote energization of the load 16, therelay 42 including contacts 34 need not be provided. The load 16 may bedeenergized by opening the switch 12.

The circuit modification shown in FIGURE 4 is similar to that shown inFIGURE 3, in that the switches 26 and 34 are normally open contacts ofrelays 38 and 42 respectively. In the circuit modification shown in FIG-URE 4, the relays 38 and 42 are remotely controlled in response to sonicand supersonic vibrations of a gaseous medium surrounding the controlcircuit. Typically this gaseous medium would be the air in the room inwhich the control circuit is utilized. The operation of thecircuit'shown in FIGURE 4 is similar to that of FIGURE 3, but for themanner in which the relay actuating coils 40 and 44 are energized.

A transducer 50 is provided to convert vibration of a gaseous mediuminto an electrical output signal. The transducer 50 is provided with apickup device 52 which is eifective to provide an electrical signal toleads 54 and 56 in response to sonic and supersonic vibrations of thesurrounding air. The pickup device 52 might be a microphone which isresponsive to both sonic and supersonic vibrations. An amplifier andfilter circuit 58 of conventional design is energized through leads 60and 62 from the AG. supply. Leads 54 and 56 from the pickup device 52provide the input to the amplifier and filter circuit 58. The output ofthe amplifier 58 appears on output leads 64 and 66. The series resonantcircuit comprising actuating coil 40' of relay 38, and capacitor 46, andthe series resonant circuit comprising actuating coil 44 of relay 42,and capacitor 48, are connected in parallel between output leads 64 and66.

In the presence of a sonic or supersonic vibration of the airsurrounding transducer 50, it will produce an electrical output signalon leads 64 and 66 having a frequency proportional to the sonic orsupersonic vibration frequency. Thus, the resonant frequency of theseries resonant circuit comprising actuating coil 40 and capacitor 46can be chosen such that it is energized at its resonant frequency when asonic or supersonic vibration of a first predetermined frequency occursin the air surrounding transducer 50. Similarly, the resonant frequencyof the series resonant circuit comprising actuating coil 44 andcapacitor 48 can be chosen such that it is energized at its resonantfrequency when a sonic or supersonic vibration of a second predeterminedfrequency occurs in the air surrounding transducer 50.

Thus, it is possible to turn the triac 14 on and off in response tosonic and supersonic vibrations in the air surrounding the transducer50. Such vibrations might be audible sounds produced by a person, orsupersonic sounds produced by a mechanical whistle. Further, the sonicor supersonic vibrations of the air might be created by a transducerdriven by an electronic oscillator. By installing the control circuitand load 16 enclosed within the dotted lines 2 within a lightingfixture, it is possible to provide for the energization anddeenergization of the lamp in response to a sonic or supersonicvibration of the air in the room.

Referring now to FIGURE 5, still another modification of the firstembodiment of this invention will be described. Again, those componentsof the control circuit which are similar to those shown in FIGURE 1 areassociated with the same reference numeral. In this circuit, theswitches 26 and 34 are shown as semiconductor controlled rectifiers 26"and 34". A typical semiconductor controlled rectifier is the siliconcontrolled rectifier (SCR). SCR 26" is turned on by applying a signal toits gate electrode 68. Similarly, SCR 34" is turned on by applying asignal to its gate electrode 70. While many arrangements might beprovided for applying a signal to the gate electrodes 68 and 70 of SCRs26" and 34", respectively, pulse transformers 72 and 74. Pulsetransformer 72 includes a primary winding 76 and a secondary winding 78.Similarly, pulse transformer 74 includes a primary winding 80 and asecondary winding 82. The secondary winding 78 of pulse transformer 72is connected between the gate electrode 68 and anode 84 of SCR 26".Similarly, secondary winding 82 of pulse transformer 74 is connectedbetween gate 70 and anode 86 of SCR 34".

A circuit arrangement for energizing primary windings 76 and 80 includesa signal transformer 88. Signal transformer 88 comprises a primarywinding 90 and a secondary winding 92. Primary winding 90 is energizedfrom the AC. supply through conductors 94 and 96. Primary winding 76 ofpulse transformer 72 is connected in series with the secondary winding92 of signal transformer '88 through a switch 98 and a current limitingresistor 100. Similarly, primary winding 80 is connected in series withsecondary winding 92 of signal transformer 88 by a switch 102 and acurrent limiting resistor 104.

In setting forth the operation of the circuit shown in FIGURE 5, it willbe assumed that the load 16 is deenergized, with the switches 12, 98,and 102 in their open positions. Closing switch 12 will energize thecontrol the signals are applied as shown in FIGURE 5 by circuit shownenclosed within the dotted lines 2. Until a signal is applied to gate 68of SCR 26", it will not conduct, and therefore signal will not beapplied to trigger 22 of the triac 14, so as to turn it on. Closingswitch 98 will cause primary winding 76 of pulse transformer 72 to beenergized, whereupon a signal will appear in secondary winding 78. Thissignal is applied to gate 68 of SCR 26", thereby turning it on. Aspreviously discussed, this will cause triac 14 to begin conducting andcontinue to conduct until it is turned-off in response to the turn-on ofSCR 34" The turn-on of SCR 34 is brought about by the closing of switch102. Closing switch 102 energizes primary winding of pulse transformer74, such-that a signal appears in its secondary winding 82. This signalis applied to gate 70 of SCR 34-", thereby turning it on. As previouslydiscussed, the turn-on of SCR 34" will cause capacitor 28 to bedischarged through the load 16, such that triac. 14 will turn off at thenext succeeding load current zero. Switch 98 need only be closedmomentarily, so as to turn on triac 14, since the latching feature ofthis circuit, as previously described with respect to FIGURE 1, willmaintain the triac 14 in its low impedance characteristic, even thoughthe SCR 26" is turned on only momentarily.

While use of silicon controlled rec-tifiers as switches 26" and 34" hasbeen shown, other types of semiconductor controlled rectifiers may alsobe used. Further, other types of semiconductive devices could besubstituted. for SCRs 26" and 34". For instance, NPN and PNPtransistors. The transistors could be used in either a switching mode orcontinuously variable control mode.

As particularly set forth with respect to FIGURES 1 and 2, thisinvention is directed toward the use of a semiconductive bidirectionaldevice as an AC. switch or a control circuit. To aid in describing thecircuit shown in FIGURE 1, the portion of the circuit included withindotted lines 2 was set forth as a control circuit wherein the impedance16 was the load, the energization of which was being controlled.Further, with a load connected in series with an.A.C. supply betweenterminals 8 and 10, (neither of which are shown), and with impedance 16being an impedance of small or negligible magnitude, the portion of thecircuit included within the dotted line was set forth as an AC. switch.

These characterizations of the circuit arrangement of this invention areused only as an aid in describing the invention. In the broader aspectsof this invention the circuit location of a load, the energization ofwhich is controlled by the conductive characteristic of thesemiconductive bidirectional device, is immaterial. Further, the circuitarrangement of this invention may be utilized in a circuit not includinga series connected load. For instance, it might be used to shunt a highimpedance A.C. supply to lower its output voltage.

I claim:

1 1. A control means for energizing a load from an AC. supplycomprising:

(a) a semiconductive bidirectional device having two main currentcarrying terminals and at least one additional gate treminal, saiddevice normally exhibiting a high impedance characteristic between saidtwo main terminals and exhibiting a low impedance characteristic betweensaid two main terminals in response to application of a control signalhaving at least a predetermined amplitude to said gate terminal, a firstof said main terminals and'a first terminal of the load connected to afirst junction point, a second of said main terminals and a secondterminal of the load connected to the A.C. supply,

(b) a control circuit comprising an energy storage means having at leasttwo terminals and a variable impedance means having at least twoterminals, a first terminal of said energy storage means 'and'a firstterminal of said variable impedance means connected to a second junctionpoint, a second terminal of said energy storage means connected to saidsecond terminal of said load, and a second terminal of said variableimpedance means being connected to said second main terminal, and

(c) a gate circuit connecting said second junction point to said gateterminal, whereby when the impedance of said variable impedance means isreduced below a predetermined level, the voltage appearing across saidenergy storage means, which is applied to said gate through said gatecircuit exceeds the predetermined amplitude so as to cause said deviceto exhibit a low impedance characteristic, said energy storage meansbeing effective in response to a subsequent increase of the impedance ofsaid variable impedance means above said predetermined level tothereafter supply gate signals in excess of said predetermined amplitudederived from the voltage developed across the load to said gate terminalthrough said gate circuit, whereby said device thereafter exhibits a lowimpedance characteristic so that the load is energized by the A.C.supply through said device.

2. The control means defined in claim 1 wherein said variable impedancemeans comprises an additional semiconductive device having two maincurrent carrying terminals and at least one additional control terminal,said additional semiconductive device normally exhibiting a highimpedance characteristic between its two main terminals an dexhibiting alow impedance characteristic between its two main terminals in responseto application of a control signal having at least a predeterminedamplitude to said control terminal, such that said semiconductivebidirectional device exhibits a low impedance characteristic so that theload is energized by the A.C. supply through said semiconductivebidirectional device.

3. The control means defined in claim 1 comprising in addition,

(d) a variable impedance turn-off circuit connecting said first junctionpoint to said second junction point, said turn-elf circuit normallyexhibiting a high impedance, said turn-ofi circuit being caused toexhibit a low impedance to dissipate the energy in said energy storagemeans such that said energy storage means is no longer effective tosupply gate signals in excess of said predetermined amplitude to saidgate terminal through said gate circuit, whereby said device againexhibits a high impedance characteristic thereby deenergizing the load.

4. The control means defined in claim 3 wherein said variable impedanceturn-off circuit comprises an additional semiconductive device havingtwo main current carrying terminals and at least one additional controlterminal, said additional semiconductive device normally exhibiting ahigh impedance characteristic between its two main terminals andexhibiting a low impedance characteristic between its two main terminalsin response to application of a control signal having at least apredetermined amplitude to said control terminal such that the impedanceof said variable impedance turn-off circuit is reduced, so as to exhibita low impedance to dissipate the energy in said energy storage meanssuch that said energy storage means is no longer effective to supplygate signals in excess of said predetermined amplitude to said gateterminal through said gate circuit, whereby said device again exhibits ahigh impedance characteristic thereby deenergizing the load.

5. The control means defined in claim 1 wherein said variable impedancemeans is a pair of contacts of a resonant reed relay, said resonant reedrelay comprising said pair of contacts and an actuating coil, saidactuating coil actuating said contacts in response to the applicationthereto of a signal of a predetermined frequency, whereby said device iscaused to exhibit a low impedance characteristic.

' a capacitor being addition, a transducer responsive to sonic andsupersonic vibrations of a gaseous medium to produce an alternatingcurrent output the frequency of which is proportional to the frequencyof the vibrations, said actuating coil being energized by thealternating current output, said trans ducer providing an output of saidpredetermined frequency, whereby said device is caused to exhibit a lowimpedance characteristic.

7. The control means defined in claim 1 wherein said variable impedancemeans is a pair of contacts of a relay including also an actuating coil,said actuating coil and connected in series across the A.C. supply, saidactuating coil and said capacitor being tuned to a predeterminedfrequency substantially higher than the A.C. supply frequency, such thatwhen a signal of said predetermined frequency is impressed on the A.C.supply, said actuating coil is energized to actuate said pair ofcontacts, whereby said device is caused to exhibit a low impedancecharacteristic.

8. The control means defined in claim 3 wherein said variable impedancemeans comprises a first pair of contacts of a first resonant reed relay,said first resonant reed relay comprising said first pair of contactsand a first actuating coil, said first actuating coil actuating saidfirst contacts in response to the application thereto of a signal of afirst predetermined frequency, and said variable impedance turn-offcircuit comprises a second pair of contacts of a second resonant reedrelay, said second resonant reed relay comprising said second pair ofcontacts and a second actuating coil, said second actuating coilactuating said second contacts in response to the application thereto ofa signal of a second predetermined frequency, whereby said device iscaused to exhibit a low impedance characteristic when a signal of thefirst predetermined frequency is applied to said first actuating coil,said device thereafter exhibiting a low impedance 6. The control meansdefined in claim 5, comprising in characteristic so that the load isenergized by the A.C. supply through said device until a signal of thesecond predetermined frequency is applied to said second actuating coil,causing said second pair of contacts to 'be actuated, such that theenergy stored in said energy storage means is dissipated such that saidenergy storage means is no longer elfective to supply gate signals inexcess of said predetermined amplitude to said gate terminal throughsaid gate circuit, whereby said device again exhibits a high impedancecharacteristic thereby deenergizing the load.

9. The control means defined in claim 3 wherein said variable impedancemeans comprises a first pair of contacts of a first relay including alsoa first actuating coil, a first capacitor, a first series circuitcomprising said first actuating coil and said first capacitor connectedacross the A.C. supply, said first series circuit being tuned to a firstpredetermined frequency substantially higher than the A.C. supplyfrequency and, said variable impedance turn-off circuit comprises asecond pair of contacts of a second relay including also a secondactuating coil, a second capacitor, a second series circuit comprisingsaid second actuating coil and said second capacitor connected acrossthe A.C. supply, said second series circuit being tuned to a secondpredetermined frequency substantially higher than the A.C. supplyfrequency, such that when a signal of said first predetermined frequencyis impressed on the A.C. supply, said first actuating coil is energizedto actuate said first pair of contacts, causing said device to exhibit alow impedance characteristic, said device thereafter exhibiting a lowimpedance characteristic so that the load is energized by the A.C.supply through said device until a signal of said second predeterminedfrequency is impressed on the A.C. supply, such that said secondactuating coil is energized to actuate said second pair of contacts todissipate the energy in said energy storage means such that said energystorage means is no longer eifectiveto supply gate signals in excess ofsaid predetermined amplitude to said gate terminal through said gatecircuit, whereby said device again exhibits a high impedancecharacteristic thereby deenergizing the load.

10. The control means defined in claim 8 comprising in addition, atransducer responsive to sonic and supersonic vibrations of a gaseousmedium to produce an alternating current output the frequency of whichis proportioned the frequency of the vibrations, said first and secondactuating coils being energized by the alternating current output, seaidtransducer providing an output of said first predetermined frequency inresponse to the presence of vibrations of a first predeterminedfrequency, and an output of said second predetermined frequency inresponse to the presence of vibrations of a second predeterminedfrequency, whereby said device is caused to exhibit a low impedancecharacteristic when a signal of the first predetermined frequency isapplied to said first actuating coil, said device thereafter exhibitinga low impedance characteristic so that the load is energized by theA.-C. supply through said device until a signal of the secondpredetermined frequency is applied to said second actuating coil,causing said second pair of contacts to be actuated, such that theenergy stored in said energy storage means is dissipated such that saidenergy storage means is no longer eltective to supply gate signals inexcess of said predetermined amplitude to said gate terminal throughsaid gate circuit, whereby said device again exhibits a high impedancecharacteristic thereby deenergizing the load.

11. The control means defined in claim 1 wherein said semiconductivebidirectional device is a bidirectional triode thyristor, said energystorage means is a capacitor, and said variable impedance meanscomprises a resistor and a switch connected in series.

12. The control means defined in claim 3 wherein said semiconductivebidirectional device is a bidirectional triode thyristor, said energystorage means is a capacitor, said variable impedance means comprises aresistor and a switch connected in series, and said variable impedanceturn-off circuit is a switch.

13. The control means defined in claim 1 wherein said semiconductivebidirectional device is a bidirectional triode thyristor, said energystorage means is an inductor, said variable impedance means comprises aresistor and a switch connected in series.

14. The control means defined in claim 3 wherein said semiconductivebidirectional device is a bidirectional triode thyristor, said energystorage means is an inductor, said variable impedance means comprises aresistor and a switch connected in series, and said variable impedanceturn-off circuit is a switch.

15. An alternating current switch comprising a semiconductivebidirectional device having two main current carrying terminals and atleast one additional gate terminal, said device normally exhibiting ahigh impedance characteristic between said two main terminals such thatthe switch is normally open in the absence of a control sig nal, andexhibiting a low impedance characteristic between said two mainterminals such that the switch is closed in response to application of acontrol signal having at least a predetermined amplitude to said gateterminal, a control circuit including in series an energy storage meansand a variable impedance means, a gate circuit having terminalsconnected respectively to said gate terminal and to a point in saidcontrol circuit intermedi ate said storage means and said variableimpedance means, and a second circuit including said main terminals andan impedance traversed by current traversing said main terminals, saidsecond circuit being connected in parallel with said control circuit,said gate terminal receiving a control signal in excess of saidpredetermined amplitude through said variable impedance means andthrough said gate circuit when the impedance of said variable impedancemeans is reduced below a predetermined level to cause said device toexhibit a low impedance characteristic to develop a voltage across saidimpedance, said energy storage means being effective in response to asubsequent increase of the impedance of said variable impedance meansabove said predetermined level to thereafter supply control signals inexcess of said predetermined amplitude derived from the voltagedeveloped across said impedance to said gate terminal through said gatecircuit.

16. The alternating current switch defined in claim 15 wherein saidvariable impedance means comprises an additional semiconductive devicehaving two main current carrying terminals and at least one additionalcontrol terminal, said additional semiconductive device normallyexhibiting a high impedance characteristic between its two mainterminalsand exhibiting a low impedance characteristic between its twomain terminals in response to application of a control signal having atleast a predetermined amplitude to said control terminal, whereby saidsemiconductive bidirectional device exhibits a low impedancecharacteristic between its two main terminals such that the switch isclosed.

:17. The alternating current switch defined in claim 15 comprising inaddition, a variable impedance turn-ofi circuit connected in circuitwith said energy storage means, said turn-off circuit normallyexhibiting a high impedance, said turn-off circuit being caused toexhibit a low impedance to dissipate the energy in said energy storagemeans such that said energy storage means is no longer elfective tosupply control signals in excess of said predetermined amplitude to saidgate terminal through said gate circuit, whereby said device againexhibits a high impedance characteristic, such that the switch isopened.

18. The alternating current switch defined in claim 17 wherein saidvariable impedance turn-ofi' circuit comprises an additionalsemiconductive device having two main current carrying terminals and atleast one additional control terminal, said additional semiconductivedevice normally exhibiting a high impedance characteristic between itstwo main terminals and exhibiting a low impedance characteristic betweenits two main terminals in response to application of a control signalhaving at least a predetermined amplitude to said control terminal suchthat the impedance of said variable impedance turn-off circuit isreduced, so as to exhibit a low impedance to dissipate the energy insaid energy storage means such that said energy storage means is onlonger effective to supply gate signals in excess of said predeterminedamplitude to said gate terminal through said gate circuit, whereby saidbidirectional device again exhibits a high impedance characteristicthereby opening the switch.

19. The alternating current switch defined in claim 15 wherein saidvariable impedance means is a pair of contacts of a resonant reed relay,said resonant reed relay comprising said pair of contacts and anactuating coil, said actuating coil actuating said contacts in responseto the application thereto of a signal of a predetermined frequency,whereby said device is caused to exhibit a low impedance characteristicbetween its two main terminals such that the switch is closed.

-20. The alternating current switch defined in claim 19 comprising inaddition, a transducer responsive to sonic and supersonic vibrations ofa gaseous medium to produce an alternating current output the frequencyof which is proportional to the frequency of the vibrations, saidactuating coil being energized by the alternating current output, saidtransducer providing an output of said predetermined frequency inresponse to the presence of vibrations of a predetermined frequency,whereby said device is caused to exhibit a low impedance characteristicbetween its two main terminals such that the switch is closed.

21. The alternating current switch defined in claim 15 adapted for usewith an alternating current supply, wherein said 'variable impedancemeans is a pair of contacts of a relay including also an actuating coil,a capacitor,

said actuating coil and said capacitor being connected in series acrossthe alternating current supply, said actuating coil and said capacitorbeing tuned to a predetermined frequency substantially higher than thealternating current supply frequency, such that when a signal of saidpredetermined frequency is impressed on the alternating current supply,said actuating coil is energized to actuate said pair of contacts,whereby said device is caused to exhibit a low impedance characteristicbetween its two main terminals such that the switch is closed.

22. The alternating current switch defined in claim 17 wherein saidvariable impedance means comprises a first pair of contacts of a firstresonant reed relay, said first resonant reed relay comprising saidfirst pair of contacts and a first actuating coil, said first actuatingcoil actuating said first contacts in response to the applicationthereto of a signal of a first predetermined frequency, and saidvariable impedance turn-off circuit comprises a second pair of contactsof a second resonant reed relay, said second resonant reed relaycomprising said second pair of contacts and a second actuating coil,said second actuating coil actuating said second contacts in response tothe application thereto of a signal of a second predetermined frequency,whereby said device is caused to exhibit a low impedance characteristicwhen a signal of the first predetermined frequency is applied to saidfirst actuating coil, said device thereafter exhibiting a low impedancecharacteristic so that the alternating current switch is closed until asignal of the second predetermined frequency is applied to said secondactuating coil, causing said second pair of contacts to be actuated,such that the energy stored in said energy storage means is dissipatedsuch that said energy storage means is no longer elfective to supplycontrol signals in excess of said predetermined amplitude to said gateterminal through said gate circuit, whereby said device again exhibits ahigh impedance characteristic, such that the switch is opened.

'23. The alternating current switch defined in claim 17 adapted for usewith an alternating current supply, wherein said variable impedancemeans comprises a first pair of contacts of a first relay including alsoa first actuating coil, a first capacitor, a first series circuitcomprising said first actuating coil and said first capacitor connectedacross the alternating current supply, said first series circuit beingtuned to a first predetermined frequency substantially higher than thealternating current supply frequency and, said variable impedanceturn-off circuit comprises a second pair of contacts of a second relayincluding also a second actuating coil, a second capacitor, a secondseries circuit comprising said second actuating coil and said secondcapacitor connected across the alternating current supply, said secondseries circuit being tuned to a second predetermined frequencysubstantially higher than the alternating current supply frequency, suchthat when a signal of said first predetermined frequency is impressed onthe alternating current supply, said first actuating coil is energizedto actuate said first pair of contacts, causing said device to exhibit alow impedance characteristic between its two main terminals, said devicethereafter exhibiting a low impedance characteristic so that the switchis closed until a signal of said second predetermined frequency isimpressed on the alternating current supply, such that said secondactuating coil is energized to actuate said second pair of contacts todissipate the energy in said energy storage means such that said energystorage means is no longer effective to supply control signals in excessof said predetermined amplitude to said gate terminal through said gatecircuit, whereby of said first predetermined frequency in response tothe presence of vibrations of a first predetermined frequency, and anoutput of said second predetermined frequency in response to thepresence of vibrations of a second predetermined frequency, whereby saiddevice is caused to exhibit a low impedance characteristic when a signalof the first predetermined frequency is applied to said first actuatingcoil, said device thereafter exhibiting a low impedance characteristicso that the alternating current switch is closed until a signal of thesecond predetermined frequency is applied to said second actuating coil,causing said second pair of contacts to be actuated, such that theenergy stored in said energy storage means is dissipated such that saidenergy storage means is no longer effective to supply control signals inexcess of said predetermined amplitude to said gate terminal throughsaid gate circuit, whereby said device again exhibits a high impedancecharacteristic, such that the switch is opened.

25. The alternating current switch defined in claim 15 wherein saidsemiconductive bidirectional device is a bidirectional triode thyristor,said energy storage means is a capacitor, and said variable impedancemeans comprises a resistor and a switch connecter in series.

26. The alternating current switch defined in claim 17 wherein saidsemiconductive bidirectional device is a bidirectional triode thyristor,said energy storage means is a capacitor, said variable impedance meanscomprises a resistor and a switch connected in series, and said variableimpedance turn-off circuit is a switch.

27. The alternating current switch defined in claim 15 wherein saidsemiconductive bidirectional device is a bidirectional triode thyristor,said energy storage means is an inductor, said variable impedance meanscomprises a resistor and a switch connected in series.

28. The alternating current switch defined in claim l1'7 wherein saidsemiconductive bidirectional device is a bidirectional triode thyristor,said energy storage means is an inductor, said variable impedance meanscomprises a resistor and a switch connected in series, and said variableimpedance turn-off circuit is a switch.

References Cited UNITED STATES PATENTS 3,238,390 3/1966 Pinckaers315-196 XR 3,335,291 8/ 1967 Gutzwiller. 3,3 60,713 12/1967 Howell.3,388,269 6/1968 Bertioli 32881 XR OTHER REFERENCES G.E. Applicationnote titled Triac Control for AC Power, written by E. K. Howell, datedMay 1964, pp. 4-6.

ARTHUR GAUSS, Primary Examiner. STANLEY T. KRAWSZEWICZ, AssistantExaminer.

US. Cl. X.R. 307-305; 315196

1. A CONTROL MEAND FOR ENERGIZING A LOAD FROM AN A.C. SUPPLY COMPRISING:(A) A SEMICONDUCTIVE BIDIRECTIONAL DEVICE HAVING TWO MAIN CURRENTCARRYING TERMINALS AND AT LEAST ONE ADDITIONAL GATE TERMINAL, SAIDDEVICE NORMALLY EXHIBITING A HIGH IMPEDANCE CHARACTERISTIC BETWEEN SAIDTWO MAIN TERMINALS AND EXHIBITING A LOW IMPEDANCE CHARACTERISTIC BETWEENSAID TWO MAIN TERMINALS IN RESPONSE TO APPLICATION OF A CONTROL SIGNALHAVING AT LEAST A PREDETERMINED AMPLITUDE TO SAID GATE TERMINAL, A FIRSTOF SAID MAIN TERMINALS AND A FIRST TERMINAL OF THE LOAD CONNECTED TO AFIRST JUNCTION POINT, A SECOND OF SAID MAIN TERMINALS AND A SECONDTERMINAL OF THE LOAD CONNECTED TO THE A.C. SUPPLY, (B) A CONTROL CIRCUITCOMPRISING AN ENERGY STORAGE MEANS HAVING AT LEAST TWO TERMINALS AND AVARIABLE IMPEDANCE MEANS HAVING AT LEAST TWO TERMINALS, A FIRST TERMINALOF SAID ENERGY STORAGE MEANS AND A FIRST TERMINAL OF SAID VARIABLEIMPEDANCE MEANS CONNECTED TO A SECOND JUNCTION POINT, A SECOND TERMINALOF SAID ENERGY STORAGE MEANS CONNECTED TO SAID SECOND TERMINAL OF SAIDLOAD, AND A SECOND TERMINAL OF SAID VARIABLE IMPEDANCE MEANS BEINGCONNECTED TO SAID SECOND MAIN TERMINAL, AND (C) A GATE CIRCUITCONNECTING SAID SECOND JUNCTION POINT TO SAID GATE TERMINAL, WHEREBYWHEN THE IMPEDANCE OF SAID VARIABLE IMPEDANCE MEANS IS REDUCED BELOW APREDETERMINED LEVEL, THE VOLTAGE APPEARING ACROSS SAID ENERGY STORAGEMEANS, WHICH IS APPLIED TO SAID GATE THROUGH SAID GATE CIRCUIT EXCEEDSTHE PREDETERMINED AMPLITUDE SO AS TO CAUSE SAID DEVICE TO EXHIBIT A LOWIMPEDANCE CHARACTERISTIC, SAID ENERGY STORAGE MEANS BEING EFFECTIVE INRESPONSE TO A SUBSEQUENT INCREASE OF THE IMPEDANCE OF SAID VARIABLEIMPEDANCE MEANS ABOVE SAID PREDETERMINED LEVEL TO THEREAFTER SUPPLY GATESIGNALS IN EXCESS OF SAID PREDETERMINED AMPLITUDE DERIVED FROM THEVOLTAGE DEVELOPED ACROSS THE LOAD TO SAID GATE TERMINAL THROUGH SAIDGATE CIRCUIT, WHEREBY SAID DEVICE THEREAFTER EXHIBITS A LOW IMPEDANCECHARACTERISTIC SO THAT THE LOAD IS ENERGIZED BY THE A.C. SUPPLY THROUGHSAID DEVICE.